Steel and process for its production



Nov. 6, 1934. P. KUHN s'rm m mocnss Fon Irs Pnonuc'rron 4 Sheets-Sheet l Filed Aug, 29, 1930 M/mers of Test Pieces Loa qao

lumber: of esf Pieces Sm AND PROCESS FOR ITS PROM Filad Aug. 29 1.9m 4 Sheets-Sheet 2 75m/rr roffzr/fs of sra-Ls Armen/NG ra 7m' .fret/4L .orar/D120@ Pmss.

NOV. 6, 1934. P KUHN 1,979,629

STEEL AND PROCESS FOR ITS PRODUCTION Filed Aug. 29, 1930 4 Sheets-Sheet NOV. 6, 1934. -P KUHN STEEL AND PROCESS FOR ITS PRODUCTION Filed Aug. 29, 1950 MGM 0 rw N FHM #El E wn; ww www n mwa f M EMM W i ym N 0r upa t c 4M y m w HM y .u f wm n m m a e 4. z o m D11/ardor: P /Qw /4 H Patented Nov.. 6, 1934 UNITED STATES PATENT OFFICE many, assgnor to Vereinigte Stahlwerke Aktiengesellschaft, Dusseldorf, Germany Application August 29, 1930, Serial No. 478,749 In Germany September 14, 1929 Claims.

This invention relates to a process for obtaining steel of high tenacity and low sensitivity to cold shortness, ageing, and brittleness at blue heat in basic open hearth furnaces.

Considered from the point of view of the chemical reactions taking place in the bath or melt, basic open hearth smelting processes are auto oxidation processes. The foreign constituents in the melt are oxidized depending upon their afnity for oxygen and to an extent determined by the concentration and temperature and pass into the slag or into the waste gases. As the concentration of reducing substances in the bath decreases the iron also is oxidized to ferrous and ferrie oxide to an increasing extent, especially towards the end of the smelting operation. Inasmuch as ferrie oxide (FezOa) is unstable in the presence of metallic iron and of the reducing substances present in the bath at the high temperatures obtaining in the smelting furnace the bulk of the oxidized iron consists of ferrous oxide (FeO). vlerrous oxide is soluble to a certain extent in the slag and also in the molten metal, the degree of distribution of same in the slag and in the bath being determined by the Nernst partition co-efcient. The concentration of ferrous oxide in the bath has therefore a certain direct relationship to that in the slag and it is therefore possible to draw comparative conclusions from the concentration of the metallic oxide in the slag, as to the extent to which the metallic oxides have dissolved in the bath.

l"Ehe fundamental reason for the continuous progress of the lining operation in basic open hearth furnaces is according to Mars probably to be attributed to the fact that the constructional materials of the furnace and the slag-forming constituents of the basic open hearth furnace, i. e. magnesia and lime cannot enter into chemical combination with the ferrous oxide of the bath, but can only form physical solutions with the metallic oxides, so that the reactive power of the dissolved ferrous oxide with the carbon in the bath remains unaffected, and the boiling-up and r lining operations therefore proceed continuously.

ls the concentration of reducing substances in the bath decreases the ferrous oxide content of the slag and also that of the bath increases rapidly towards the end of the smelting process on account of the oxidizing action of the gases. As is known, test bars of steel., taken from the bath at this period usually exhibit red shortness on bending at a red heat to a greater or lesser degree.

Dichmann, a Wel1-known authority on the operation of basic open hearth furnaces, considers (Cl. 'l5-27) that a stat-e of equilibrium with respect to the ferrous oxide content in the slag and the reducing substances in the iron is reached for all practical purposes when the ferrous oxide content of the slag has been reduced to 13% FeO (corresponding to Fe). At the same time the slag also contains about the same quantity of MnO. As is taught by practical experience however, it is not always possible in the ordinary course of working to produce-steel having a low carbon content underneath a slag containing only 10% of iron without undue difliculty; usually the iron content of the slag is somewhat higher.

When the desired carbon content has been obtained the ning process must be brought to a finish-forcibly to a certain extent-by the addition of deoxidizing agents. As is known the chief problem of deoxidizing is to remove the residual oxygen which exists in a state of equilibrium in the bath with carbon. The deoxidizing agents chosenapart from carbon which is only used in exceptional cases--are ferrous alloys, the metallic constituents of which on account of their great amnity for oxygen as compared with that possessed by iron, are able to remove said oxygen. All the deoxidizing agent's with the ex ception of carbon, form solid or liquid products which are partly retained in the iron in a finely divided heterogeneous condition throughout the solidification period and constitute a portion of the known non-metallic constituents of the steel. These constituents reduce the technical properties of the steel as is known and lead to the production of longitudinal cracks and sensitivity on hardening and when the steel is subjected to varying stresses they are usually the starting points for fatigue fracture. For this reason according to Eilender deoxidation with agents which produce solid deoxidation products, should be avoided as far as possible.

A further drawback of the usual deoxidation processes towards the end of the smelting operation is the fact that when employing ferro-manganese for example it is impossible completely to remove the oxygen even when using large quantities of the deoxidation agent, for invariably only a definite state of equilibrium can be reached. Experiments have therefore been carried out using gradual deoxidation with metals which exhibit a progressively increasing ainity for oxygen, and it is possible in thisA manner by adding large quantities of aluminium for example, to produce steel with a very small content of oxygen. The Adisadvantages of this deoxidizing process still persists however, because the oxidation llU ge amounts of lime perature rises thus setting free metallic s in the slag and effecting reducing substances in the quantity of lime added varies natum under the working connt case the amount of lime -2% (this amount After the lime has is further raised as ag is kept as mobile ease the velocity of ne between the slag crease the absorptive ontent of the slag is running down, whilst ns large quantities of The MnO uced in a bath until the slag and remely small l` y cases up to 1.3% Operating with a high- 1; equires an elevated and throughout the whole which may be assured for exgeneral with- Additions of any deobviously be made in 1;

the furnace, during ugh or in the pan. y perceptible amount s very quietly as the :Fe-i-CO gas, cang to the amount of the acids in the ombined;

charge.

g for further amounts of lime.

40%, this amount being lower at mperatures, the MnO is vigorous- 1 sferred to the bath. The reduced tatu nascendi reduces theferrous in the steel very vigorously, the

FeO-1-C y transformed into the molten state and the ulk of the manganese has been oxidized and ransformed into the slag, lar are added according as the tem ove the usual level,

ides from compound e reduction by the to be added varies between 1 been added the temperature rapidly as possible and the sl as possible in order to incr reaction in the reaction zo manganese in s oxide dissolved tinuously reduced at the same time.

finally the ferrous oxide content of bath has been reduced to an ext deoxidation by means of the manganese reduce rom out of the slagin man of manganese and over. ly basic slag naturally r uniform temperature' melting operation, ample by using the regenerative furnaces described in Patent 1,421,259.

When the desired concentration of carbon has been reached the melt is tapped off without the usual deoxidation process, i. e. in out any further additions. sired alloy constituents can the usual manner either in the tapping off in the tro On account of the lack of an of oxygen the steel solidie reaction:-

h gives rise to the formation of not occur.

p already relatively low on y of by he run whic TABLE 1 products rally accord process form increasing with rising furnace temperatures) of r races of oxygen ,simon is Since the ferrous oxide c Xidation specially high te The imge is inasmuch as y upon ontent.

4. 4 5 1 1 1|. 20 502 260911 170% Sw937868ww 0.010101 211171910191719101 1 3 1 62 23 22903109 w 00 @4.4987601 111.21111010171101 0000 115m a a 94 23 584 20607 11.1%00 250wm13203 1 1 1 1 1 1 1211131611101 6l Qu 1450880 2800 w5000175 1111 11111316111 0000 1w214 m0 14 2 3 73920805 890.0 @35793781 1111 111111019101 0000 H1780@ 1 Z6 7 3 5 5 1830 1 1 1 1 1 1 1 1 1 1 121 1 0000 M1581w620 64 033 8 997016 @900 m744871 1111 111211911411 0000 M18 13620 78 233 63065720 480 036524.30 11.1r111117161101 0000 m1661100 71W.u 672761390 4800 141881453 1111 111111711611 0000 w19 03620 60W@ 040 02043 5700 092 60011 1111 111111171614101 0000 MOB 02 3 4 A. 1 6 5347 ammo waenoezo 11011 111110116101 00 0 109H0263 016 245058556 W5 M 460258581 1111 1111171111 0000 w02016w0 6 30G 60 4m79006 1 1 1 1 1 15191 1 mOvwllU 30 If the foregoing statements be considered as 5 a whole, basic open hearth smelting processes ab usually formed which are readily retained slag to be c tion of the lining process, typical the amOllnt 0f the The present process occupies an intermediate osition between the acid and the basic Open ferrous ox1de content of the slag being also conocesses, inasmuch as it forcibly It is also known to add large quantities of manganese to the charge when it is desired to According to the process of the present invenon this rule is deliberately disregarded and when the charge has been com- Chemical composition of preliminary test portions of steel and slag taken from melt A Constituent control of the desulphurizing process and the creases considerably in parallel to this automatic product of aluminium, i. e. alumina is retained pletel very readily by steel in a finely dispersed condition after the ,manner of an emulsion.

can be looked upon as processes with automatic ox oxidation of the molten metal bath and induced th indirect deoxidation bythe addition of ferrous bath. The

alloys, whereby solid or liquid oxidation l0 are by the steel. On the other hand according to ditions of the prese Mars the crucible smelting process and in a similar manner the acid open hearth after the compl examples of a process with automatic deoxidation. During the acid process when definite conditions are maintained the last t in the steel existing as FeO form a stable chemical compound of iron silicate with the silica of and the bath and also t0 in 20 the lining which passes into the slag. At the same Capacity 0f the Sla time owing to the action of the pure iron reduced from the lining and this silicon takes u the remaining traces of oxygen. According to moreover the Slag Contal Mars, the excellent properties of "acid steel can be M1101 about attributed partly to this automatic de by Virtue of which only very small quantities of 1y reduoed from out of the Slag and the manilnpurity or even no impurities at all are retained gallese 1S tron by the steel.

hearth smelting pr effects in the basic process a certain automatic formed by this feaotlon 1S agom Tod deoxidation during the whole smelting process by Cycle by the Carbon Content of the means of manganese in a similar manner to the role of the silicon in the acid furnace.

portant part played by the manganese during the amount. The manganese content of the bath inusual deoxidation shortly beforetapping is known per se.

smelt a high value steel. However when producing soft steel in the basic open hearth furnace the percentage of manganese in the char kept as far as is possible below 1.5%

Killing has shown that the exploitation of manganese and consequent thereupon the econom the process are reduced very considerabl still further increasing the manganese c large quantities of oxygen are prevented from combining with the steel even during the smelting processwhich is to be carried out as rapidly, as possible in View of the oxidationmeans of a large charge of manganese, since t manganese is first converted into slag to a preponderant extent. After the melt has been down completely,

so p

5o ti TABLE 2 Chemical composition of preliminary test portions of steel and slag taken from melt B Constituent 1 2 3 4 5 6 7 8 0 l0 ll 10,05 10,80 13, 17,80 18,20 10,30 10, 34 18 20 17 45 10,30 0, 18 0, 32 0, 23 0, 04 0, 50 o, 72 0, 73 0f 72 0: 73 0, 7s 11, 00 11,03 10. 10 10,20 10,31 8,84 8, 93 s, 98 8, 40 8, 30 1, 00 1,14 1,14 0, 74 1, 4e 1, 02 0, 73 0, 73 1, 59 3, 42 2, 50 2, 00 2, 13 1. 85 1, 32 1, 53 0, 71 0, 05 1, 01 1, 37 18, 00 22, 41 30. 12 28, 70 20, 50 33, 40 35, 27 35, 30 37, 49 30, 10 0,00 0,00 3,41 0,80 0,10 9,12 8,75 0,00 0,51 10,02 30, 33, 04 28, 78 23, 57 28, 47 25, 72 24, 55 24, 32 22, 74 22, 51

. hardness.

Tables 1 and 2 give as examples of the hereinbefore described process, analyses taken every minutes of test portions of steel and slag taken from the furnace, Table 1 being for a soft metal (A) and Table 2 being for a melt B of medium The charge consisted in both cases of about of steel-iron containing 4 to 5% of manganese, of soft scrap core iron, the remainder being sheet scrap. The course of the variation in the Vamounts of the most important constituents such as carbon and manganese in the case of the steel, and MnO, CaO, and FeO in the case of the slag is illustrated in the case of melt A in Figure l, and in the case of melt B in Figure 2.

Figs. 1 and 2 respectively show in melts A and B the variation of the chemical composition of steel and slag during the melting process;

Fig. 3 shows the tenacity properties of steels produced according to the special deoxidizing.

process;

Fig. 1 shows tenacity properties of ordinary carbon steel;

Fig. 5 shows notch tenacity of 20 mm. steel from melt A.;

Fig. 6 shows notch tenacity of standard 20 mm. boiler plate;

Figs. 'l and 8 show notch tenacity of 20 mm. plate from melt B and standard steel 48-22 mm. diameter, respectively.

In Figures 1 and 2 the two series of ordinates represent the percentage of carbon and manganese in the steel and the percentage of FeO, MnO and CaO in the slag respectively, whilst the abscissae represent the numbers of the test-pieces.

Melt A was run down with a carbon content of 0.76%. Soon after it had been run down considerable quantities of lime and some fluor-spar were added at short intervals. As the lime content of the slag increased and the temperature rose and the carbon content decreased, an extremely violent reduction of MnO in the slag took place. As

i the concentration of MnO decreased the concentration of manganese in the steel increased until test No. 'l showed a concentration of 0.90%. Concomitant with the reduction of manganese, deoxidation which was not quite uniform took i place, and the FeO content in the slag was re- Melt B (Table 2 and Figure 2) was somewhat more dicult to run down than melt A. After the first test portion had been taken 500 kilogrammes of lime were added in consequence of which the CaO content rose rapidly to 30%. After tests 5-9 100 kgs. of lime were added each time, whereupon the CaO content increased to about the temperature rising at the same time. From test 2 onwards vigorous reductions of the manganese from the slag tool: place. The MnO content of the slag was reduced to 23%, the FeO content was already very low after running down and during the course of the smelting operation it sank apparently uniformly to about 8% on tapping. The red shortness tests and notched bar impact tests carried out during the course oi the smeltlng process were satisfactory. The steel solidified absolutely quietly. The automatic dcoxidation can therefore be considered as being complete, when the FeO content of the slag prior to tapping is at the maximum 10%, whilst the manganese content of the steel is rising uniformly. No limitation at all exists with respect to the carbon content in the nal product as is shown from the attached documents. The process is applicable with the same security and advantage to the production of soft and medium hard or hard steel whether it be unalloyed or alloyed.

The technical properties of steel produced in accordance with the present invention are characterzed essentially by a, high elongation and notched bar tenacity in comparison with the tensile strength. These steels are at the same time practically insensitive to stresses due to ageing, working at a blue heat and other harsh treatment in working routine. Figure 3 gives the' mean values for the results of numerous tensile strength tests on the products produced by the present process. Figure 4 gives tensile strength properties of the ordinary open hearth steel.

In these lgures tensile strength and elastic limit in kgs. per mm2 and elongation and reduction of area as percentages are plotted against the percentage of carbon contained in the steel.

As can be recognized from Figure 3 the values for the elongation and the notched bar tenacity are greater than those of the ordinary carbon steels particularly in the case of steels of medium hardness. In the case of the elongation the increase amounts to about 5 units, whilst the notched bar tenacity is about 100% greater. The steels were tested in the normalized condition.

As is known the sensitivity to ageing is specially inuenced by the concentration of oxygen dissolved in the iron. The steels manufactured by the present process are in practice very deficient in respect of the sensitivity to ageing.

lll() Since as is known the eifect of ageing treatment consists substantially in a displacement of the steep drop in the notched bar tenacity-temperature curve in a direction of higher temperatures, the gauging of the ageing effect produced at normal temperatures is facilitated by examining the notched bar tenacity of the steelv prior to and subsequent to'ageing treatment at elevated and at low temperatures. tests carried out by the applicant the test pieces having dimensions of 10xl1x60 mm. were upset by means of a stamp to the extent of about 10%. were annealed for one hour at 250 C., and were subsequently subjected to notched bar tenacity tests and were examined at temperatures ranging from to 200 C. The dimensions of the test pieces were then 10x10x60 mm. each having a semicircular notch 5 mm. in depth and 2 mm. across. In Figure 5 the results of notched bar ageing tests carried out upon test pieces taken from the centre of a 20 mm. sheet from melt A are given in dependency upon the testing temperature. Figure 6 contains the results of tests carried out under similar conditions upon ordinary boiler sheet metal of the same tensile strength. Similarly in Figures 7 and 8 results of notched bar tests carried out on a. heat-treated 20mm. sheet taken from melt B and by Way of comparison results upon a 22 mm. cylindrical rod made of ordinary open hearth steel of the same tensile strength are given.

In Figures 5, 6, 7, and 8 the notched-bar tenacity in mkg. per sq. cm. beforeand after ageing treatment is plotted against the testing temperature. The full line gives the result when the test-bar is subjected to heat treatment at 900 C. for one hour, and is cooled in the air. The thin line gives the result when the test-bar is subjected to'heat-treatment for one hour at 900 C., is cooled in the air, is upset tothe extent of 10% and annealed.

As is shown in Figure 5 the steep drop of the curve prior to the ageing treatment begins at -20 C.; at 50 C. the sheet steel still has a notched-bar tenacity of 6 mkg. persq. cm.

The steep drop of the curve is displaced by virtue of the ageing treatment by about 30 in the direction of more elevated temperatures, the fall begins at 0 C. and is consequently not yet perceptible at room temperature. The notched bar tenacity at room temperature is thus merely lowered from 11.4 down to 10.9 mkgs. per sq. cm. by the ageing treatment. The sheet metal is substantially insensitive to ageing. Figure 6 shows results of tests carried out on ordinary boiler sheet metal. In the unaged condition the steep drop begins at room temperature. By virtue of the ageing treatment such drop is displaced by almost 100 in the direction of more elevated temperatures with the result that the sheet metal up to testing temperatures of 50 C. is brittle. The notched bar tenacity at room temperature has thus been lowered from 11 down to about 1 mkg. per sq. cm. In the case of melt B the notched bar tenacity at room temperature is reduced by the ageing treatment from 9 to 8.2 mkgs. per sq. cm. and in the case of ordinary carbon steel from 8.5 to 2.5 mkgs. per sq. cm., i. e. a substantially greater reduction.

Steels produced in accordance with the present invention are for practical purposes free from segregation phenomena and have a very low oxygen content. It has been shown as the result of exhaustive experiments that they have an ex- In the ageingA tremely high resistance to the action of overheating, recrystallization and fusion welding, which tend to increase the size of the grain.

1. A-two-period process oi' producing a steel of high tenacity and low sensitivity to cold brittleness, ageing and blue shortness in a basic open hearth furnace, which comprises oxidizing manganese during the first of said periods and transferring said manganese into the slag and then continuously reducing manganese from theslag and continuously increasing the manganese content of the steel throughout the second period, thereby transferring the reduced manganese from the slag into the bath so that the process is terminated without adding ferro-manganese as a deoxidizing agent before the tapping.

2. A process of producing steel of high /tenacity and low sensitivity to cold brittleness, ageing. and blue shortness in `a basic open hearth furnace, consisting in transferring manganese into the slag during an oxidation period, raising the temperature and adding basic materials to reverse the transformation of the manganese, thereby continuously reducing and transferring manganese from the slag into the bath during the entire period calculated from the reversal of the transformation to the tapping so that the process is terminated without` adding ferro-manganese as a deoxidizing agent before the tapping.

3. A process of producing a steel of high tenacity and low sensitivity to cold brittleness, ageing and blue shortness in a basic open hearth furnace, consisting in transferring manganese into the slag during an oxidation period, raising the temperature and adding lime to reverse the transformation of the manganese, thereby continuously reducing andI transferring manganese from the slag into the bath during the entire period calculated from the reversal of the transformation to the tapping so that the process is terminated without adding ferro-manganese as a. deoxidizing agent before the tapping.

4. A process of producing a steel of high tenacity and low sensitivity to cold brittleness, ageing and blue shortness in a basic open hearth furnace, consisting in transferring the bulk of the manganese contained in the bath into the slag during the oxidation process, adding basic materials and continuingA to raise the temperature, thereby reversing the transformation of the manganese and continuously reducing and transferring manganese from the slag into the bath during the entire period calculated from `the reversal of the transformation to the tapping so'that the process is terminated without adding ferromanganese as a deoxidizing agent before the tapping.

5. A process of producing a steel of high tenacity and low sensitivity to cold brittleness, ageing and blue shortness in a basic open hearth furnace, consisting in transferring the bulk of the manganese contained in the bathinto the slag during the oxidation process, addinglime and continuing to raise the temperature thereby reversing the transformation of the manganese and continuously reducing and transferring manganese from the slag into the bath during the entire period calculated from the reversal of the transformation to the tapping so that. the process is terminated without adding ferro-manganese as a deoxidizing agent before the tapping.

PAUL KHN.

AGI 

